Roller skis are used for ski training in the off season when there is no snow. Such training must simulate skiing on wet snow and on dry, powdery snow. Roller skis are also used by many non skiers for a low impact aerobic exercise. In order to duplicate the energy expenditure of snow skiing it is desirable to have relatively slow wheels on such roller skis. The rolling speed is mainly a function of the energy return of the tire material on the wheels. Tires made with low rebound, high energy absorbing materials offer more rolling resistance but they can become extremely hot and often fail prematurely. In such cases entire wheels must be replaced, all too frequently. Conversely, tires made with high rebound, low energy absorbing materials offer little rolling resistance but these wheels roll too fast and do not properly simulate skiing on snow. In order to duplicate the energy expenditure of snow skiing it is desirable to have slow wheels without having the heating problems normally associated therewith.
As the popularity of in-line skating grows, more and more people are using in-line skates for purposes other than purely recreational skating. Several different categories of skaters and skates have evolved. For example, there are aggressive skates, speed skates, hockey skates, and many levels of recreational and fitness skates. Those people familiar with in-line skating often transition from recreational skating to fitness skating as they become more experienced therewith.
Many experienced fitness and speed skaters use their in-line roller skates for conditioning and endurance training. However, because the wheels and bearings of in-line skates offer little or no resistance, skaters must travel at very high speeds to achieve a desired heart rate and muscular conditioning. Many skaters do not wish to travel at the high speeds required for such training. Further, it is often difficult to safely travel at high speeds when skating on a busy bicycle path or street.
Thus, there is a need for means to vary the rolling resistance of one or more of the wheels used on roller skis to simulate skiing on different types of snow, such as wet snow or powdery snow, or on in-line roller skates to accommodate different exercise routines.